Natural Disaster

A major weather event wipes out most of the inhabitants.

Anime Examples:

Poverty

Extreme poverty in society has the poor in utter seclusion from the rich. The poor live dilapidated homes in the slums where rampant human trafficking, murder, gang violence, and other cruel deeds run amok. There are low morale when the poor think they have no hope for a better future.

Anime Examples:

War

War tears families, society, and countries apart as two nations, race, or clans fight each other over territory, rights, money, and more. Morale is usually low with everyone disillusioned. A lack of trust and hope looms over everyone.